1. Field of the Invention
This invention relates to an optical recording medium, such as a magneto-optical disk. More particularly, it relates to a recording medium of the type in which a recordable area, often called a RAM area, and a read-only or reproduce-only area, often called a ROM area, are provided on a single medium.
2. Related Art Statement
An optical recording medium for data recording is known. For example, in a magneto-optical disk, a tracking guide groove or grooves are provided on the disk in the form of a helix or concentric circles. Data is adapted to be recorded on or reproduced from the recording track along the track direction by taking advantage of the photomagnetic effects of the disk material, with the previously formed guide groove or grooves or the lands between the grooves used as the recording track. Data is recorded or reproduced photomagnetically under a tracking servo based on optical detection of the guide grooves. In such a case, addresses and data are recorded alternately on the recording track, and data control is achieved on the basis of this address data, so that data having a specific address is recorded or reproduced on a block-by-block basis or a sector-by-sector basis.
It would be convenient for users and producers of software if data which is only to be read and not rewritten, such as an operating system or a basic dictionary, could be supplied in a pre-recorded form on an otherwise recordable medium. For this reason, a recording medium, such as a disk or a card, has been developed on which a read-only area (a so-called ROM area) and a recordable area (a so called RAM area) are provided together.
FIG. 1 shows an example of a magneto-optical disk as a recording medium on which the data which is only to be read is previously recorded. In this figure, a recordable, or RAM, area 2 on which signals can be recorded and a read-only, or ROM, area 3 are provided on the magneto-optical disk 1. In the RAM area 2, the preformed guide grooves or lands between the guide grooves are used as the recording tracks on which data is recorded photomagnetically. FIG. 1 shows part of two adjacent recording tracks, marked 4A and 4B. These can be adjacent parts of the same recording track if the recording track is in the form of a spiral. In the ROM area 3, tracks are formed in which data which is only to be read is previously recorded by pre-formatting, for example in the form of pits. FIG. 1 shows parts of two adjacent recording tracks, marked 5A and 5B. These can be adjacent parts of the same recording track if the recording track is in the form of a spiral.
However, in such a magneto-optical disk 1, the signals received by the tracking servo at the time of scanning the ROM area 3 may be based on pits as, for example, in the method disclosed in U.S. Pat. No. 3,876,842. Thus, since the tracking servo normally reproduces information from the RAM area 2 photomagnetically, the servo must be switched between the different formats of the RAM area 2 and the ROM area 3.